Accuracy of femoral head center reconstruction using a straight cementless rectangular stem: An in-silico study comparing elderly and middle-aged patients

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Introduction: Accurate reconstruction of the femoral head center (FHC) is essential for restoring hip biomechanics in total hip arthroplasty (THA). Previously described age-related morphological changes-such as canal widening and a mediocaudal FHC shift-may complicate anatomical reconstruction in all age-categories using a single non-modular cementless stem. This study assessed the capacity of such implant to achieve adequate FHC reconstruction across age groups and sexes. Methods: Virtual implantation of a non-modular cementless stem (SL-PLUS™) was performed in CT-based 3D reconstructions of 148 femora from middle-aged (<80 years) and very elderly (≥80 years) subjects. For each case, the optimal implant size, type (standard or lateral), and modular head (-4 mm, 0 mm or +4 mm) were selected. FHC deviation was measured in three dimensions; reconstructions were considered adequate if < 5 mm in all directions. Results: Overall, 92.4 % of reconstructions were considered adequate. No significant differences in reconstruction accuracy could be detected between age or sex groups. Very elderly males required significantly larger stem sizes than middle-aged males (mean size 6.4 vs. 5.1; p < 0.001). Lateralized stems were used more frequently in very elderly males (76.0 %) than in middle-aged males (44.4 %; p = 0.001). Reconstruction failure occurred in 11 cases, mostly due to a reduced mediolateral offset in femora with high native ML-offsets and/or low neck-shaft angles (8 out of 11 cases). Conclusions: A single non-modular cementless stem enables satisfactory FHC reconstruction in most patients, regardless of age or sex. However, certain anatomical configurations may exceed its reconstructive capacity. Careful preoperative planning is essential to identify cases that may need an alternative approach.

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